From the manufacturer

Women's ColdGear Base 4.0 Crew

UA Base 4.0 is built for extreme cold weather and lower activity. It uses a unique pattern that's designed to trap heat without adding bulk. Think long underwear, revamped for today's top athletes.

• UA Base 4.0 Extreme Baselayer is our warmest yet, delivering extreme warmth in the extreme cold
• Fitted: Streamlined fit that’s not too tight or too loose.
• Soft, brushed grid interior traps air against your skin, closely managing your body's microclimate to keep you warm & comfortable
• Material wicks sweat & dries really fast
• 4-way stretch material moves better in every direction